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Hydrovac internal leak
#1416730 Mon Jul 12 2021 05:49 PM
Joined: Aug 2012
Posts: 24
P
PeteP Offline OP
'Bolter
I"ve been scratching my head for some time now on where my brake fluid is going -- master cylinder is about half empty every time I run her but no leaks in the lines, wheel cylinders, master cylinder -- nothing. Brake pedal takes a pump or two at first but then holds a nice pedal and the truck stops just fine. Until yesterday that is when I put on the brakes a little heavy and so much white smoke billowed out the tailpipe I couldn't see the end of the truck. My guess is the hydrovac is dumping brake fluid into the vacuum system and the engine is burning it up. I understand that some parts are still available for the hydrovac although I've not yet started my search.

Questions: 1) How much boost does the hydrovac give? Mine is a parade truck and, although I totally agree that stopping is mandatory the most I haul is the wife, a cooler and a couple chairs. Can I just bypass the hydrovac at least temporarily, and still stop reasonably? 2) I like to consider myself a decent antique mechanic but I've never been into a hydrovac before. Any advice for a first time rebuilder of such things?

Thanks

Pete P.
Harborcreek, Penna.

Re: Hydrovac internal leak
PeteP #1416774 Mon Jul 12 2021 11:47 PM
Joined: Feb 2016
Posts: 547
7
'Bolter
Hi Pete, I rebuilt all of my 6 wheel cylinders and the master cylinder, replace all steel lines with cupro-nickel and all new rubber hoses. I have no leaks and a great peddle. I bypassed the hydro-vac by running the line from the master directly to the first tee. My truck weighs 7200 lbs. empty and I haul 110 bales of hay a couple of times a year and I'm happy with the brakes. You have to get used to them and keep an eye on traffic 'cuz you won't be locking up the brakes but no trouble bringing it to a stop. With that all said my truck tops out at 45 MPH due to the 7.20:1 rear axle so speed is a factor here.


1957 Chevrolet 5700 LCF 283 SM420 single speed rear, 1955 IH 300U T/A, 1978 Corvette 350 auto
Re: Hydrovac internal leak
PeteP #1416784 Tue Jul 13 2021 12:56 AM
Joined: Mar 2004
Posts: 5,276
M
'Bolter
What year and size is your truck?

If a child runs in front of your truck during a parade you'll be glad you have a working hydrovac.

The Hydrovac provides a 35% increase in line pressure, so if 78buckshot uses 100 pounds of leg pressure to stop his truck you'll get the job done with 65 pounds of leg pressure.

NAPA used to carry rebuilt units...and there are companies that rebuild then for you. For me for the ~$300 cost, it's not worth not having it working.

Mike B smile

Re: Hydrovac internal leak
PeteP #1416794 Tue Jul 13 2021 01:40 AM
Joined: Dec 2007
Posts: 158
D
'Bolter
Hey Pete. It’s there for a good reason. As someone who works around heavy equipment, and I know it’s different, safety isn’t something worth gambling on. The Berns Company (Gary Kirpluk) sells rebuild kits for $75 (although that was probably more than five years ago now). There are parts to deal with but the rebuild itself is pretty straight forward. If you need any help or detailed pics of anything, let us know! And once done, there’s almost no maintenance associated with (maybe a couple drops of mineral oil in the drum each year). #stovebolt.com #payingitforward

Derek

Re: Hydrovac internal leak
PeteP #1416806 Tue Jul 13 2021 04:31 AM
Joined: Aug 2018
Posts: 615
2
'Bolter
The hydrovac system is fail safe to resorting to normal brake operation if it fails.
Often on old trucks the hydrovac is long inoperable junk but the brakes still work okay
I have three farm trucks In this state, 2 tons and up all factory hydrovac all haven’t had proper service in perhaps 40 years and the basic brakes work with no assist.
These trucks are not drive on the road obviously.
With no load good brakes will let you lock up the tires no problem in panic braking
So don’t worry about Sunday parades
It’s safe for that without the hydrovac
You want the hydrovac when you are tailgating In modern traffic with a full load
Which you shouldn’t be doing in the first place
-s

Re: Hydrovac internal leak
PeteP #1416914 Wed Jul 14 2021 02:36 AM
Joined: Dec 2020
Posts: 113
2
'Bolter
We had our hydrovac rebuilt at a company in Chicago. "Rebuilders Inc.". They did a great job, and I highly endorse them.

Steve

Re: Hydrovac internal leak
PeteP #1416915 Wed Jul 14 2021 02:38 AM
Joined: Dec 2020
Posts: 113
2
'Bolter
By the way, our hydro also leaked into the vacuum side and down to the check valve.

Steve

Re: Hydrovac internal leak
PeteP #1416939 Wed Jul 14 2021 01:51 PM
Joined: Dec 2018
Posts: 931
F
'Bolter
PeteP Fix your hydrovac for safetys sake,once done a little bendix vacuum cylinder oil 2x a year and you''ll have brakes.My 2 are 71 yrs. old and with service work fine,read the service book use hydraulic jack oil from your local flaps. Always fun to climb on the brakes and know you can stop !!

Re: Hydrovac internal leak
PeteP #1416956 Wed Jul 14 2021 05:44 PM
Joined: Oct 2019
Posts: 7
D
'Bolter
Rock Auto will set up an RMA with A1 Cardone in TX and will provide you a shipping label to send your hydrovac in for a rebuild. Takes a few days. The hydrovac makes a HUGE difference in braking. I don't mean to sound like a nanny, but I can't imagine the conversation with the insurance company if you get in a wreck and disabled your factory brake booster and that's why I had mine rebuilt.

Re: Hydrovac internal leak
DntKnwWhatImDoin #1416959 Wed Jul 14 2021 06:01 PM
Joined: Aug 2012
Posts: 24
P
PeteP Offline OP
'Bolter
Sorry, forgot the truck particulars -- it's a '46 2T (6400.)

Sounds like parts aren't that expensive and the rebuild is, hopefully, straightforward. I'm pleasantly surprised that there are still commercial rebuilder options available too.

As I mentioned above, I agree completely with the 'stopping is mandatory' logic. If repair were impractical that's one thing but it sounds like this won't be that bad.

Thanks all,

Pete P.
Harborcreek, Penna.

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